Field
This invention relates generally to an insert for an electrical connector and, more particularly, to an electrically dissipative polymer insert for an electrical connector that encapsulates multiple pins in the connector and allows electrostatic discharge of the pins, but is still compliant with stringent resistance requirements of various government and industry connector standards.
Discussion
Small electrical circuits, referred to herein as microcircuits, typically include very small electrical circuit elements and are used for many applications, for example, telecommunications circuits, consumer electronic circuits, etc. One specific application for such microcircuits includes high-speed data communications devices on a spacecraft. These types of microcircuits often employ one or more multi-pin connectors and cables to connect the microcircuit to other circuits. A typical multi-pin connector generally includes an insert made of a highly insulating dielectric having a high resistivity that prevents current paths between the pins and between the pins and an outer enclosure of the connector that is typically connected to chassis ground. These types of microcircuits are often susceptible to electrostatic discharge (ESD), which has the capability of damaging the microcircuits and rendering them at least partially inoperative. One significant problem is the risk that the damage to the microcircuit from electrostatic discharge is not catastrophic, where the microcircuit may later experience failure, such as for example, when on orbit.
During spacecraft assembly, many communications cables are connected to data terminals and multi-pin connectors, where if the cable has electrostatic charge, that charge could discharge into the connector causing damage to the circuit. Thus, significant steps are often taken in this and other assembly environments to prevent such electrostatic discharge. In order to prevent electrostatic discharge damage to a circuit when connecting a cable, it is known in the industry to first discharge the cable connector by connecting each pin in the connector to a discharging device having a high resistance element. Further, workers may be required to wear special clothing and take other steps to reduce the chance of electrostatic discharge.
Various techniques have been attempted in the industry to modify connector construction to mitigate or reduce electrostatic discharge. For example, connector designs have been proposed that employ discharge gaps, metallic grounding strips, discharging pins, discharging clips, discharging devices, dissipative discs, dissipative layers and dissipative surfactants. However, most of these techniques have been less than effective. In the discharge gap design, gaps are fabricated around the pins in the connector so that if the electrostatic charge voltage is high enough, the charge will arc across the gap to a conductor thus dissipating the charge. However, such a connector is difficult to fabricate, and has the drawback that sparking during connecting a connector is undesirable. In addition, the discharge gap designs are typically only effective when the electrostatic discharge results in a high voltage greater than 5000 volts, where modern sensitive microelectronics often have an electrostatic discharge sensitivity of less than 500 volts. Further, discharging pins significantly change the design of a standard connector construction that could make the new connector incompatible with cables that these devices are supposed to be mated with. Also, the effectiveness of a dissipative surfactant is a strong function of humidity in the air. In a dry climate, these surfactants become less affective for dissipating electrostatic charge build-up. Also, surfactants can wear off during the course of connector service life. In the space industries, most of the dissipative surfactants are regarded as surface containments and are prohibited from being used in space flight hardware.
It has previously been proposed in the prior art to provide a voltage-varying resistive polymer in a connector to discharge electrostatic voltages. However, the specifics of the polymer that has the voltage-varying resistance has not been identified, and polymers used, for example, in a poly-tantalum capacitor does break down at a high voltage whether or not it will discharge voltage build-up in the process. Other polymers may carbonize or be charred so that a carbon rich conductive path may develop and alleviate a voltage build-up. However, this process is irreversible and the conductive path may become permanent after the discharge event.